1. Field of the Invention
This invention pertains to a repellant for the well-documented insect pests of the beetle family Scolytidae. Specifically, 4-allylanisole, a component of the resin of the preferred target of the scolytids, Pinus, and other conifers, has been identified as a repellant for the southern pine beetle (SPB), Dendroctonus frontalis Zimm., and related scolytid pests. This repellant can be used to protect potential host trees from attack by scolytids.
2. Background of the Prior Art
Infestation of conifers by scolytids has been well documented. Considerable attention has been devoted to protection of high-value stands, as well as single trees, threatened by SPB and other scolytids for the preservation of wildlife, cultural and recreational resources. This focused attention on biorational tactics has been largely devoted to efforts using synthetic semiochemicals, in particular, the insects own anti-aggregation or inhibitor pheromones such as verbenone, Payne et al, Journal of Applied Entomology, 114:341-347 (1992).
There has also been substantial attention devoted to analysis of the method and sequence of attack by the SPB and other scolytids on the target trees. While the process of selection is not well understood, it appears that "pioneer" insects (e.g., females in Dendroctonus spp. and males in Ips spp.) initiate the attack on susceptible host trees, and conspecifics follow in response to attractant pheromones such as frontalin. Secondary pheromones, including inhibitory pheromones, are also involved.
The trees respond to this attack by secreting resins. The resins secreted have been the subject of a variety of studies. Numerous chemicals have been identified in the resin, one of which is 4-allylanisole, also known by a variety of chemical synonyms, including estragol(e), methyl chavicol, methoxyallylbenzene and tarragon. The presence of this phenylpropanoid compound has been identified among a wide variety of terpenes and resin acids.
4-allylanisole was targeted as a potential inhibitor of fungal growth, of which growth is believed necessary for successful SPB infestation. Bridges, Phytopathology, 77:83-85; January, 1987. The Bridges reference speculates with respect to the impact of 4-allylanisole on the SPB but provides no data and does not suggest repellant activity.
Other researchers have focused on the action of other terpenes in the pine resin, and while noting the presence of 4-allylanisole, have not ascribed to any particular activity with respect to the various bark beetles targeted. Representative articles include Renwick et al., "Systems of Chemical Communication in Dendroctonus", Contributions from Boyce Thompson Institute, 24:283-292, 1970.; Werner, Journal of insect Physiology, 18:423-438, 1972; Pierce et al., Journal of Chemical Ecology, 13:1525-1542, June, 1987; Salom et al., Journal of Chemical Ecology, 17:2527-2538, December, 1991; and Salom et al., Journal of Applied Entomology, 114:472-479, 1992. Of these references and studies, Werner is perhaps the most complete. The Werner article concludes that 4-allylanisole, therein identified as methyl chavicol, is an attractant for the Ips grandicollis, stimulating, after purification, a 90 percent response rate at a 1.0 percent concentration value among male beetles and a 50 percent response rate among female beetles.
Current measures for protecting loblolly pine and other potential host trees from scolytid infestation remain inadequate. Although three compounds (chloropyrifos, fenitrothion, carbaryl) in addition to lindane are now registered for use against bark beetles, increased federal restrictions may curtail their use in the future. These traditional chemical insecticides can be used to protect high value trees (Amman, "Integrated Control of the Mountain Pine Beetle in Lodgepole Pine Forests", Proc XVI, IUFRO World Congr. Norway, pp 439-446, 1976), although carbaryl is not effective against SPB (Berisford et al., "Efficacy Studies: Prevention", USDA Forest Serv. Gen Tech Report SE-21, pp 3-8, 1981). However, the high cost of labor and the products, and the need to spray all surfaces of the bole for effective control will always restrict the use of topically applied chemicals (Billings, "The Southern Pine Beetle", Chapter 10, USDA Agrig. ESPBRAP, For. Serv., SEA. Tech. Bull. No. 1631, 1980). In addition, relying solely on chemical sprays, especially the use of only one or a few, increases the risk of development of resistance in the pest population (Pimentel et al., "Effects of Single Versus Combinations of Insecticides on the Development of Resistance", Environ. Entomol. 14:582-589, 1985). Other inherent detrimental effects are associated with the use of these insecticides. Their use reduces the quality of the environment, and alters the ecosystem by reducing species diversity, modifying the food chain, and altering patterns of energy flow and nutrient cycling (Pimentel et al., "Pesticides and Ecosystems", BioScience 32(7):595-600, 1982). Many of these effects can persist for long periods. For example, lindane can be very persistent in the environment (residues remaining on logs one year after treatment and washed in water for 2 hours still exceed the tolerance threshold of fish) (Austra, "Lindane Residues on the Bark of Sprayed Logs", Norwegian For. Res. Instit. Report 3184, 8 pp, 1984). Insecticides may adversely affect natural enemies. All of these registered chemicals have serious impacts on natural enemies and soil arthropods (e.g., [Williamson et al , "Impact of Insecticidal Control on the Southern Pine Beetle Population in East Texas, J. Econ. Entomol. 64:1140-1144, 1971]; [Carter et al., "Seasonal Abundance of Certain Soil Arthropods in a Fenitrothion-Treated Red Spruce Stand", Can. Entomol. 105:1065-1073, 1973]; [Hoy et al., "Effects of Lindane, Chlorpyrifos and Carbaryl on a California Pine Forest Soil Arthropod Community", Environ. Entomol. 10:732-740, 1981]; [Swezey et al , "Comparative Toxicity of Lindane, Carbaryl, and Chloropyrifos to Western Pine Beetle (Dendroctonus brevicomis) (Coleoptera: Scolytidae) and Two of its Predators, Enoclerus iecontei (Coleoptera: Cleridae) and Temnochila chlorodia (Coleoptera: Trogostidae)", Can. Entomol. 114:397-401, 1982]; and [Werner et al., "Laboratory and Field Evaluation of Insecticides Against The Spruce Beetle (Coleoptera: Scolytidae) and Parasites and Predators in Alaska", J. Econ. Entomol. 76:1144-1147, 1983]). The most widely used semiochemical, verbenone, an anti-aggregation pheromone, fails to inhibit a large number of attacks and has little or no effect on female SPB (Salom et al., "Effect of Verbenone Enantiomers and Racemic endo-Brevicomin on Response of Dendroctonus frontalis (Coleoptera: Scolytidae) to attractant-baited traps", Can. J. For. Res. 22:925-931, 1992).
Accordingly, it remains a goal of those skilled in the art to establish a more effective means of protecting loblolly pines and other conifers from attack by SPB and related pests, preferably without the introduction of a chemical foreign to the established parameters of the infestation process.